Various communication systems may benefit from suitable use of redundancy. For example, surveillance systems in avionics applications may benefit from having functional redundancy. A system can include a collision avoidance or alerting system function in wired connection to a directional antenna. The system can also include a first mode-S transponder function in wired connection to the directional antenna. The system can further include a second mode-S transponder function in wired connection to the directional antenna, wherein the first mode-S transponder function is independent from the second mode-S transponder function.